In electrochemical treatment such as, for example, electroplating or the like, oil and fat portion and oxide film on the surface of metal as substance to be treated are removed by degreasing cleaning and acid pickling in its pretreatment step. In doing so, the metal surface is activated so that a good metal film can be coated on the metal surface.
The degreasing and cleaning is executed in such a manner as to dip a substance to be treated in an aqueous alkali solution, while the acid pickling is executed in such a manner as to dip a substance to be treated in an acidic aqueous solution which is prepared by diluting sulfuric acid or hydrochloric acid. Thereafter, the substance to be treated is cleaned with water. Then, an acidic or alkaline chemical is put into the waste water to neutralize it and thereafter, the neutralized water is discharged from the factory.
Accordingly, the conventional pretreatment step requires a specific bath vessel and a specific water cleaning vessel. Thus, the equipment becomes large in scale, and various kinds of chemicals and a large quantity of water are required. Thus, the treatment cost is increased. Moreover, a water cleaning step is required between the degreasing treatment step and the acid pickling step, Thus, long time is required and productivity is lowered. In addition, heavy metal such as lead, zinc and the like cannot be removed in the neutralizing treatment. Thus, a water discharge equipment is required and so, the equipment cost is increased.
Moreover, in the conventional pretreatment step, work is forced to do under such inferior circumstances that the treatment solution is scattered and toxic gas is generated. In addition, there is such a problem that the substance to be treated is risked to get hydrogen brittleness by hydrogen gas which is generated in the acid pickling step. So, it is required another means for removing the hydrogen brittleness.
In order to solve those problems, Japanese Patent Application Laid-Open No. 2000-7319 discloses a method in which a solution containing phosphine as an organic solvent is utilized, a substance to be treated is dipped in this solution or this solution is coated on the substance by a brush or spray, thereby removing oil and fat portion and oxide film without a need of dangerous and/or toxic chemicals such as strong acid, cyan, etc and without substantially collapsing a base material.
However, the above-mentioned phosphine is expensive so that the production cost is increased and in addition, the oil and fat and the oxide film can not be removed to the satisfactory extent.
Incidentally, there are disclosed cleaning methods as a method for cleaning semiconductors, precision machine parts, etc., for example, in Japanese Patent Application Laid-Open Nos. 2000-308862 and H11-207276 among others, in which a supercritical fluid and a subcritical high concentration fluid are utilized as a cleaning solvent.
The former method can cope with the removal of oil and fat stuck to machine parts, etc. but it can not cope with the removal of oxide film formed on the machine parts, etc. In that case, another step for removing the oxide film is required. Thus, productivity is decreased and the equipment cost is increased.
The latter method includes a compressor capable of generating supercritical carbon dioxide, a heater, a reaction container capable of receiving therein a substance to be treated and an oil and fat portion recovery tower for releasing the supercritical state and having an oil and fat recovery member filled therein, those components being connected to each other through a circulation pipe.
The supercritical carbon dioxide is fed into the reaction container to remove the oil and fat portion stuck to the substance to be treated. Thereafter, the supercritical carbon dioxide with the oil and fat portion dissolved therein is fed into the oil and fat portion recovery tower where the pressure is reduced to release the supercritical state so that the oil and fat portion is recovered. On the other hand, the liquid-state or gas-state carbon dioxide, from which the oil and fat portion has been recovered, is fed into the compressor to generate, once again, the supercritical carbon dioxide and the supercritical carbon dioxide thus generated is reutilized.
However, although the above-mentioned method can cope with the removal of oil and fat portion stuck to the machine parts, etc., it can not cope with the removal of oxide film formed on the machine parts, etc. In that case, another step for removing the oxide film is required. Thus, productivity is decreased and the equipment cost is increased. Moreover, the oil and fat portion recovery member of the oil and fat portion recovery tower is clogged with the passage of time and therefore, replacement is required.
Moreover, as another method, there is known a method in which carbon dioxide as a cleaning medium is pressurized and the pressurized carbon dioxide is jetted from a cleaning gun so as to be thermally expanded. Then, dry ice in the form of particle is sprayed to the surface of the member to be cleaned, so that the oil and fat portion stuck to the surface of the member is blown off.
However, here again, this method can cope with the removal of oil and fat portion but it can not cope with the removal of oxide film. Moreover, there is such a problem that after the dry ice is sublimated, it is released to the air.
It is a primary object of the present invention to provide, in order to solve the above-mentioned problems, a method for activating a surface of a base material and an apparatus thereof, which is suited to be utilized for pretreatment in electrochemical treatment such as, for example, electroplating and the like, and in which an oxide film removing solution having a desired acidity concentration can easily and inexpensively be prepared with an inexpensive material.
Another object of the present invention is to provide a method for activating a surface of a base material and an apparatus thereof, in which the surface of a base material such as metal can be subjected to degreasing treatment and oxide film removing treatment simultaneously, efficiently and rationally, in which productivity can be enhanced and the equipment cost can be reduced.
A further object of the present invention is to provide a method for activating a surface of a base material and an apparatus thereof, in which utilized treatment solution is rationally processed so that it can be reutilized and safety of its discharge is ensured.
A still further object of the present invention is to provide a method for activating a surface of a base material and an apparatus thereof, in which utilized treatment solution is rationally processed and the treatment solution is effectively recovered so that the recovered treatment solution can be reutilized and safety of its discharge is ensured.